1. Field of the Invention
This invention relates to a candle having a wick surrounded by a combustible core in turn surrounded by a transparent shell.
2. Description of the Prior Art
A conventional candle, which can include a fragrance, is made of petroleum paraffin or waxy materials such as beeswax and tallow. More recently, hydrocarbon gels, gelling agents with oil, and polyamides have been used as candle base materials.
The use of polyamide in clear candles started in the 1970s as disclosed in U.S. Pat. Nos. 3,615,289 (1971) and 3,819,342 (1974) and German specification 2,357,567 (1974). More recently, a low molecular weight, ester-terminated polyamide, was blended with a liquid hydrocarbon to form a transparent composition having gel consistency and stated to be useful as a candle base material, as disclosed in U.S. Pat. No. 5,783,657 and PCT International application WO 98/17243 (both 1998). However, candle made of this composition show a sticky surface and low resistance to shear stresses.
The use of polyamide resins in combination with one or more 12-hydroxystearic acid ester solvents in a clear solid candle is disclosed in U.S. Pat. No. 5,882,363, (1999). In this case, the mechanical properties are better, but the burning presents a poor performance, with the formation of black pools and drowning of the wick.
It is accordingly an object of the invention to provide a candle that overcomes the disadvantages and drawbacks of the prior art as outlined above while affording a favorable combination of esthetic, mechanical, and burning characteristics.
In accordance with this invention, there is provided a candle comprising at least one wick surrounded by a core having a top surmounted by said at least one wick, a bottom, and sides, and comprising a combustible candle core composition which is surrounded by a non-sticky, shear resistant, and clear transparent shell comprising a combustible candle shell composition comprising at least 81% by weight of at least one dimer acid based polyamide resin and 0-19% by weight of at least one solvent for said polyamide resin.
A candle according to the invention can be presented as a self-supporting stand alone candle (a so-called xe2x80x9cpillarxe2x80x9d candle) or as a candle in a container, where the shell itself can constitute the container. The core within can be contiguous with the shell or removably placed within, with a gap of predetermined width between the shell and the core.
The candle according to this invention can be of any desired size and shape. In particular, a candle according to the invention can be higher than it is wide, or wider than it is high. The candle according to the invention can be uniform in cross-section or vary in cross-section along its height.
Thus, the core-shell construction of a candle according to the invention is particularly suitable for creating a great variety of esthetically pleasing and decorative shapes for the candle of the invention, including cylindrical, spherical, polygonal, tear-drop and free-form abstract shapes as well as human and animal shapes (such as a hand, a torso, or the head of a cat) and shapes of familiar inanimate objects (such as a telephone or a replica of a well-known building). The shell surrounds the core for at least 50% of its height and can extend up to the full height of the core and even higher, thus constituting a shade surrounding the flame when the candle burns.
The relative dimensions of the shell and the core in the candle according to the invention are defined such that the shell is at least 2 mm thick. The thickness of the shell need not be uniform throughout. The upper limit for the dimensions of the shell is defined such that the dimension of the shell as a fraction of the combined dimensions of the shell and the core measured outward from the wick can be up to 75% of the combined dimensions.
The term xe2x80x9ccombustiblexe2x80x9d is used in its conventional meaning to indicate that the material burns when ignited in the ordinary manner of a candle. The term is not used in its regulatory sense as promulgated by the US Department of Transportation to indicate a material having a flash point in a defined range. In fact, candles according to the invention desirably have a flash point higher than that of a regulatory xe2x80x9ccombustiblexe2x80x9d material.
The terms xe2x80x9cclearxe2x80x9d and xe2x80x9ctransparentxe2x80x9d are used with their conventional meanings to indicate that object placed behind or within a candle (for example the wick or a decorative icon) can be discerned by a viewer. The term xe2x80x9cvisually compatiblexe2x80x9d is used to indicate that the combustible composition of the invention is clear and transparent as defined.
The term xe2x80x9cdimer acidxe2x80x9d is used to designate a known product obtained under dimerization conditions from unsaturated fatty acids having 15 to 21 carbon atoms, such as oleic acid, linoleic acid, and linolenic acid, and containing predominantly dicarboxylic acids having 30 to 42 carbon atoms, along with minor amounts of monocarboxylic acids and tricarboxylic acids, as well as hydrogenation products thereof.
The shell is made of a composition based on one or more dimer acid based polyamide resins that is transparent and that is compatible with the candle material making up the combustible candle core, and serves to contain the core material in the form of a candle. The shell can be scented or unscented, colored and/or decorated as desired or plain, with or without inclusions.
The dimer acid based polyamide resin can be a neutral or slightly acidic (i.e. not amine-terminated) polyamide having a molecular weight in the range from 1000 to about 60000 daltons, as obtained, for example, from the polymerization of a diamine with one or more dicarboxylic acids of which at least one is dimer acid as defined. Dicarboxylic acids which can be included in the polyamide according to the invention include oxalic acid, succinic acid, glutaric acid, adipic acid, 2-methylglutaric acid, azelaic acid, sebacic acid, isophthalic acid, and terephthalic acid. Diamines which can be included in the polyamide according to the invention include ethylenediamine, propylene-1,2-diamine, 1,6-diaminohexane, piperazine, N,Nxe2x80x2-bis(2-aminoethyl)piperazine, and ether-interrupted alkylenediamines such as the polyoxyalkylenediamines disclosed, for example, in U.S. Pat. No. 6,077,900 here incorporated by reference.
Dimer acid based polyamide resins in which dimer acid is at least in part hydrogenated are particularly preferred.
The solvent when present is a non-resinous substance, which can be liquid or solid at ambient temperature, of high polarity, low polarity, or intermediate polarity, or a mixture of such substrates, that is miscible with the polyamide component of the combustible candle shell composition, such that up to 19 parts by weight of the solvent can be admixed with 81 or more parts by weight of polyamide and afford a clear composition at the intended use temperature (usually the normal ambient temperature) of the candle according to the invention. To remain part of the shell composition throughout its useful life the solvent should have a boiling point of at least 180xc2x0 C.
High polarity solvents include saturated and unsaturated alcohols having 8-24 carbon atoms, ether alcohols having 6-36 carbon atoms, aliphatic carboxylic acids having 8-24 carbon atoms as well as amides and bis-amides of such carboxylic acids. Low polarity solvents include hydrocarbons having 10-50 carbon atoms. Intermediate polarity solvents include ethers and carboxylic acid esters having 10-60 carbon atoms.
The combustible candle core according to the invention can be made of a combustible composition the is the same as the shell composition, or of a different combustible composition such that any interactions that occur between the shell and the core do not adversely affect the favorable properties of the shell or the core, in particular the transparent appearance, mechanical sturdiness, and non-sticky feel of the shell. The core can be, but need not be, transparent. When the core composition and the shell composition are different, the core composition has a softening temperature no higher than that of the shell composition. Preferably the shell composition has a softening temperature at least 10xc2x0 C. higher than that of the core composition.
The shell composition and the core composition can each be colored as desired. Striking visual effects can be obtained when the shell and the core compositions are of different colors.
The combustible candle core can, accordingly, be made of any conventional combustible candle composition, for example that of a typical beeswax or paraffin base candle. More particularly, the core composition comprises at least one ingredient selected from the group consisting of fatty acids having 14 to 24 carbon atoms, fatty acid esters of polyhydric alcohols, paraffins, polyamide resins, and waxes. The combustible candle core can also be made of the non-paraffin candle composition disclosed in commonly assigned U.S. Pat. No. 6,063,144 whose entire disclosure is here incorporated by reference.